A pattern is a replica of a cast metal object.
It is used to prepare the cavity into which molten material will be poured during the casting process.
Patterns used in sand casting may be made of wood, metal, plastics or other materials. Patterns are made to exacting standards of construction, so that they can last for a reasonable length of time, according to the quality grade of the pattern being built, and so that they will repeatedly provide a dimensionally acceptable casting.
Many factors have to be taken into consideration when designing a pattern to ensure the best and most cost-effective results.
For example, some designs are simple and allow for easy removal from the mold. However some castings are complex and require careful pattern design / manufacture which can include the need for core assemblies to ensure patterns can be removed easily from the molds.